Abstract

Microburst can produce downdraft and strong divergent outflow wind, whose characteristics are distinct from those of the atmospheric boundary layer (ABL) wind. The current research is directed to simulation of microburst phenomenon and study of the microburst-wind loading effects on different civil structures using laboratory and numerical simulations and scaled models. In the first part, the steady impinging jet model was comprehensively studied by using a 2-feet-diameter laboratory microburst simulator that can generate a steady impinging jet. Point and Particle Image Velocimetry (PIV) measurements were both conducted. Comparisons suggest that the average wind velocity profile matches well with those derived from field data and previous research. The transient features of impinging jet and cooling source models were studied and compared by performing numerical simulations. Results showed that the cooling source model could produce a reasonable instantaneous radial velocity profile at maximum wind condition, while the transient impinging jet model resulted in some deviation from the field data. Merits and demerits of each modeling method are presented. The second part of this study relates to the microburst-wind loading effects on different civil structures such as low-rise buildings, an agro-storage structure, and a high-rise building by deploying the microburst simulator to simulate steady-impinging jet flow over geometrically-scaled models. The effects of important parameters, such as the distance of the model from the center of the microburst, the model geometry, and the orientation of the building with respect to radial outflow of the oncoming microburst-like wind, on the surface pressure distributions as well as the resultant wind loads acting on the test models were assessed quantitatively. Detailed results on both mean and fluctuating wind loads were discussed and compared to those obtained in conventional straight-line or Atmospheric Boundary Layer (ABL) wind. Finally, a numerical simulation using a commercial CFD code was performed to simulate the microburst flow field and its wind loading effects on a low-rise building and a high-rise building in full scale, utilizing an improved impinging jet model and a cooling source model with temporal and spatial inlet parameters. The macroscopic flow features of the flow field and their comparison with previous numerical, laboratory and field data suggest that by eliminating the strong shear at the jet interface, the improved impinging jet model can generate a reasonable simulation of the transient microburst flow field, similar to that of the cooling source model. Since the cooling source model that has more resemblance to the real microburst is difficult to replicate in the laboratory, the improved impinging jet model as studied here can be considered as an alternative to the steady-impinging jet model commonly used in the laboratory studies, in the future.